JP2000280342A - Polylactic-acid-series shrink-sheet-like matter and packaging material or shrink labeling material using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polylactic-acid-series shrink-sheet-like matter which has a sufficient shrinkage factor and biodegradability and, moreover, to provide the biodegradable polylactic-acid series shrink-sheet-like matter which causes no mutual fusing of labels in sterilization by heating when the matter is used for the labels of a drink bottle or the like. SOLUTION: This sheet-like matter is molded of a biodegradable polymer constituted mainly of a polylactic-acid-series polymer. In this case, the crystal melting heat quantity (ΔHm) of the polylactic-acid-series polymer is 5-45 J/g, and a difference between a crystallization heat quantity (ΔHc) generated by the crystallization of the polylactic-acid-series polymer, a constituent of the biodegradable polymer forming this sheet-like matter, on the occasion when the temperature of the sheet-like matter is raised, and ΔHm, i.e., ΔHm-ΔHc, is 5-32 J/g.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a shrinkable sheet containing a polylactic acid-based polymer as a main component.

[0002]

2. Description of the Related Art Sheets and films of polyvinyl chloride, styrene-butadiene copolymer, polyethylene terephthalate, etc. are known as heat-shrinkable sheets or films used for shrink wrapping, shrink-wrapping wrapping, shrink labels and the like. It is also widely used and consumed in industry. However, when these sheets and films are rejected in the natural environment, they remain without being decomposed due to their stability.
It causes problems such as spoiling the landscape and polluting the living environment of fish and birds.

[0003] Therefore, there is a demand for a material made of a degradable polymer which does not cause these problems.
Development is taking place. One example is polylactic acid. It is known that polylactic acid naturally undergoes hydrolysis in soil, does not remain in its original form in soil, and then becomes a harmless degradation product by microorganisms.

[0004]

However, polylactic acid is inherently brittle, so that even if it is made into a sheet or film, it does not have sufficient strength to be practically used.

On the other hand, Japanese Patent Application Laid-Open No. Hei 5-221790 discloses a heat-shrinkable film made of polylactic acid for a label.
It is a high-temperature shrinkable film that is as high as 40 to 150 ° C. and can be used as a label for a glass bottle or the like. On the other hand, in general shrink wrapping and shrink-wrapping wrapping, the packaged object is a fresh food or paper box, or various containers containing food or medicine, and to prevent denaturation or deformation of the packaged object due to heat,
Shrinking is performed at a low temperature of about 70 to 120 ° C. The above publication does not show that the heat shrinkable film for labels has sufficient shrinkage in the low temperature range. Further, even for a high-temperature shrinkable label, the shrinkage finish is poor, and a part that floats without contacting the shrinkable object is formed, so that sufficient performance may not be exhibited.

[0006] Japanese Patent Application Laid-Open No. 7-256755 discloses a heat-shrinkable film made of a polylactic acid-based polymer satisfying predetermined requirements. This heat shrink film
Although it has a low-temperature shrinkage property, if it does not shrink in a short time, it will be heat-set and will not shrink sufficiently. Furthermore, the shrinkage finish is poor, and there may be a case where a floating portion or the like does not come into contact with the object to be shrunk.

Further, when the above-mentioned heat-shrinkable film is used as a shrinkable wrapping or shrink-wrapping wrapping of a fresh food product or a paper box as a packaged object, or various containers containing foods or chemicals,
Usually, it is desired that the shrinkage is 10% or more, but a sufficient shrinkage cannot be obtained with the heat shrinkable film.

Further, when the heat-shrinkable film is used for a label such as a bottle for a beverage, the label is wound around the bottle, the beverage is filled, and heat sterilization is performed on a production line. At this time, labels of adjacent bottles may be fused together by heat.

Accordingly, the present invention provides a biodegradable polylactic acid-based shrinkable sheet having a sufficient shrinkage rate, and furthermore, when used as a label for beverage bottles and the like, when heat sterilized. An object of the present invention is to provide a biodegradable polylactic acid-based shrinkable sheet that does not fuse labels.

[0010]

SUMMARY OF THE INVENTION The present invention relates to a sheet-like material formed from a biodegradable polymer containing a polylactic acid-based polymer as a main component. ) Is set to 5 to 45 J / g, and when the sheet is heated, the heat of crystallization generated by crystallization of the polylactic acid-based polymer which is a component of the biodegradable polymer forming the sheet ( The above problem was solved by setting the difference between ΔHc) and ΔHm, that is, ΔHm−ΔHc at 5 to 32 J / g.

By using a polylactic acid-based shrinkable sheet having predetermined ΔHm and ΔHc, a biodegradable polylactic acid-based shrinkable sheet having a sufficient shrinkage can be provided. Also, when used for labels such as beverage bottles, it is possible to provide a biodegradable polylactic acid-based shrinkable sheet that does not fuse with each other during heat sterilization.

[0012]

Embodiments of the present invention will be described below.

The polylactic acid-based shrinkable sheet according to the present invention is a sheet formed from a biodegradable polymer containing a polylactic acid-based polymer as a main component.

The above-mentioned biodegradable polymer refers to a polymer having biodegradability, that is, a property degradable by microorganisms. The polylactic acid-based polymer which is a main component of the biodegradable polymer refers to lactic acid, specifically, a homopolymer of D-lactic acid or L-lactic acid or a copolymer thereof.

The polylactic acid-based polymer can be produced by a known method such as a condensation polymerization method and a ring-opening polymerization method. For example, in the polycondensation method, D-lactic acid, L-lactic acid or a mixture thereof is directly dehydrated and polycondensed to obtain a polylactic acid-based polymer having an arbitrary composition. In addition, in the ring-opening polymerization method, lactide, which is a cyclic dimer of lactic acid, is subjected to ring-opening polymerization in the presence of a predetermined catalyst while using a polymerization adjuster or the like as necessary, and polylactic acid having an arbitrary composition is obtained. A polymer is obtained. The lactide includes L-lactide which is a dimer of L-lactic acid, D-lactide which is a dimer of D-lactic acid, and DL-lactide which is a dimer of D-lactic acid and L-lactic acid.

The biodegradable polymer may be composed solely of the polylactic acid-based polymer as the main component,
A mixture of the above-mentioned polylactic acid-based polymer and a biodegradable aliphatic polyester other than the polylactic acid-based polymer may be used. The biodegradable aliphatic polyester other than the polylactic acid-based polymer preferably has a glass transition point Tg of 0 ° C. or lower. By adding a biodegradable aliphatic polyester other than the polylactic acid polymer having a glass transition point Tg of 0 ° C. or lower, when stretching the obtained polylactic acid-based shrinkable sheet,
Breakage can be prevented and shrinkage finish can be improved.

The addition amount of the biodegradable aliphatic polyester other than the polylactic acid-based polymer is
10 to 100 parts by weight per 0 parts by weight is preferred. 10
If the amount is less than the weight part, it may be broken, and furthermore, the shrinkage finish is likely to be deteriorated due to wrinkles or avatars. On the other hand, if the amount exceeds 100 parts by weight, the film is not stretched at a uniform magnification at the time of stretching, and thickness unevenness is likely to occur. When such a film is shrunk, the shrink finish tends to deteriorate.

Specific examples of the biodegradable aliphatic polyester other than the polylactic acid-based polymer include homopolymers or copolymers of hydroxycarboxylic acids other than lactic acid and copolymers of lactic acid and hydroxycarboxylic acids other than lactic acid. Polymers, aliphatic polyesters obtained from aliphatic dicarboxylic acids and aliphatic diols,
An aliphatic polyester obtained by ring-opening polymerization of a cyclic lactone, a mixture of these polymers, and the like.

Examples of the hydroxycarboxylic acids other than lactic acid include glycolic acid, 3-hydroxybutyric acid, 4-hydroxybutyric acid, 4-hydroxyvaleric acid, 5-hydroxyvaleric acid, and 6-hydroxyvaleric acid. These homopolymers or copolymers, or copolymers of these with lactic acid, can be produced by using the above-mentioned polylactic acid-based polymer polymerization method. In addition, it can be produced in cells. In this case, it is biosynthesized by acetyl coenzyme A (acetyl CoA) in cells such as alkaligenes eutrophas. An example thus obtained is poly-β-hydroxybutyric acid. Since poly-β-hydroxybutyric acid itself is insufficient in strength, it is used as a copolymer with poly-β-hydroxyvaleric acid.

Further, the aliphatic dicarboxylic acids include succinic acid, adipic acid, suberic acid, sebacic acid,
Dodecane diacid and the like can be mentioned as examples, and as the aliphatic diol, ethylene glycol, 1,4-butanediol, 1,4-cyclohexane dimethanol and the like can be mentioned. The aliphatic polyester is produced by esterifying any of these aliphatic dicarboxylic acids and aliphatic diols.

Furthermore, cyclic lactones include ε
-Caprolactone, δ-valerolactone, β-methyl-
δ-Valerolactone and the like, and the above aliphatic polyester is produced by ring-opening polymerization.

In each of the above polymerization steps, a small amount of a chain extender, for example, a diisocyanate compound, an epoxy compound, an acid anhydride or the like can be used for the purpose of increasing the molecular weight of the obtained polymer.

The above-mentioned sheet material means a sheet or a film. By definition in JIS, a sheet is a flat product whose thickness is thin and its thickness is generally small compared to its length and width, and a film whose thickness is extremely small compared to its length and width and whose maximum thickness is Is an optionally defined thin flat product, usually supplied in roll form (JI
SK 6900). Therefore, it can be said that a sheet having a particularly small thickness among the sheets is a film. However, since the boundary between the sheet and the film is not clear and cannot be clearly distinguished, in the present application, as described above, the term “sheet-like material” is used as a concept including both the sheet and the film.

The above-mentioned biodegradable polymer is formed into a flat or cylindrical unstretched sheet-like material or a sheet-like material melt by a general melt molding method such as an extrusion method, a calendering method and a pressing method. Then, this is monoaxially or biaxially stretched by a roll method, a tenter method, a tubular method, an inflation method or the like to obtain a sheet-like material.

The heat of crystal fusion of the polylactic acid-based polymer which is a component of the biodegradable polymer (abbreviated as “ΔHm”).
Is preferably 5 to 45 J / g, more preferably 20 to 40 J / g. Further, when the temperature of the sheet is raised, the heat of crystallization (“ΔH”) generated by crystallization of the polylactic acid-based polymer which is a constituent component of the biodegradable polymer forming the sheet is obtained.
c ". ) And ΔHm, ie, ΔHm
m-ΔHc is preferably 5 to 32 J / g, and 10 to 30 J / g.
Is preferred. When the ΔHm is less than 5 J / g, the obtained sheet-like material is easily fused. When it exceeds 45 J / g, the obtained sheet-like material may not easily shrink.
When ΔHm−ΔHc is less than 5 J / g, the obtained sheet-like material is easily fused. When it exceeds 32 J / g, the obtained sheet-like material may not easily shrink.

The above ΔHm is determined by heat-treating at a temperature 30 ° C. lower than the melting point of the polylactic acid-based polymer which is a component of the biodegradable polymer, and increasing the heating rate by 10% according to the method described in JIS K7122. This is the amount of heat required to melt the crystals generated in the polylactic acid-based polymer when the temperature of the sheet is raised at a rate of ° C./min. This is determined from the area of the endothermic peak due to crystal melting that appears near the crystal melting point of the polylactic acid-based polymer in the differential scanning calorimetry (hereinafter, abbreviated as “DSC”) of the sheet. The reason why the heat treatment is performed at a temperature 30 ° C. lower than the melting point of the polylactic acid-based polymer is that the heat treatment can crystallize the polylactic acid-based polymer. In this crystallized state, the temperature is raised at a predetermined heating rate and ΔHm is measured, so that a biodegradable polymer having the same composition, for example, D, L-polylactic acid having the same composition, It is possible to eliminate a difference of ΔHm which may be caused by a lot difference.

ΔHc is the amount of heat of crystallization of the above-mentioned sheet-like material, and is the amount of heat generated during the crystallization that occurs during the primary temperature increase process according to the method described in JIS K 7122. In the DSC of the sheet-like material, it is determined from the area of the heat generation peak.

The above ΔHm mainly depends on the crystallinity of the polylactic acid polymer itself, and takes a large value in a polylactic acid-based polymer having high crystallinity. Incidentally, in the case of homopoly-L-lactic acid, which is considered to have the highest crystallinity, it is about 50 J / g. ΔHc is an index relating to the degree of crystallinity of the sheet at that time. When ΔHc is large, crystallization of the sheet proceeds during the heating process, that is, the sheet before the temperature rise Indicates that the crystallinity was relatively low.
Conversely, when ΔHc is small, it indicates that the crystallinity of the sheet before the temperature rise was relatively high.

Therefore, ΔHm−ΔHc is defined as the crystallinity of the sheet-like material based on the crystallinity of the polylactic acid-based polymer which is a component of the biodegradable polymer forming the sheet-like material. Indicates the degree of conversion. Therefore, △ Hm- △ Hc
The smaller the value, the lower the crystallinity of the sheet-like material.

Therefore, as a method for lowering ΔHm−ΔHc, a polylactic acid-based polymer having low crystallinity or a sheet having a relatively low crystallinity can be used. In particular, if a sheet having relatively low crystallinity is produced from a polylactic acid-based polymer having low crystallinity as a raw material, ΔHm−ΔHc can be further reduced.
The degree of crystallinity of the sheet-like material depends to a large extent on the composition of the biodegradable polymer, but is also greatly affected by the film processing conditions.

Further, in order to reduce the crystallinity of the film in the forming process, particularly in the biaxial stretching by the tenter method, an appropriate stretching temperature and stretching ratio are selected to suppress orientation crystallization,
ΔHm−ΔHc can also be reduced by a method such as cooling to below the crystallization temperature immediately after stretching to suppress crystallization.

Examples of preferred biodegradable polymers satisfying the above-mentioned conditions of ΔHm and ΔHm-ΔHc include polylactic acid-based polymer which is a main component of the biodegradable polymer and L-lactic acid and D-lactic acid. A copolymer having a composition ratio of L-lactic acid to D-lactic acid of 98: 2 to 94: 6, or
6:94 to 2:98. With this composition ratio, a polylactic acid-based shrinkable sheet having ΔHm of 5 to 45 J / g and ΔHm−ΔHc of 5 to 32 J / g can be obtained. Thereby, the crystallinity of the biodegradable polymer becomes appropriate, and when it is formed into a sheet, sufficient shrinkage can be obtained. Can be prevented. By the way, even when the composition ratio of L-lactic acid and D-lactic acid is out of the above range, ΔHm is 5 to 45 J / g and ΔHm−ΔHc is 5
Although it is possible to obtain a polylactic acid-based shrinkable sheet having a ３２Hm- △ Hc of 5 J / g or more, it is necessary to pay attention to the selection of a stretching temperature and a stretching ratio. is there.

When a polylactic acid-based shrinkable sheet containing the biodegradable aliphatic polyester is used, the biodegradable aliphatic polyester may also have crystallinity.
In this case, when ΔHm and ΔHc are measured using this polylactic acid-based shrinkable sheet, the influence of crystals of the biodegradable aliphatic polyester affects the measured values. In this case, △ Hm is
It can be obtained by measuring using the polylactic acid-based polymer itself, which is a component of the biodegradable polymer forming the polylactic acid-based shrinkable sheet. Further, ΔHc is measured using the polylactic acid-based shrinkable sheet, and can be obtained by converting the value and deriving an amount corresponding to the polylactic acid-based polymer.

The shrinkage rate of the resulting polylactic acid-based shrinkable sheet is preferably 10% or more at 80 ° C. for 10 seconds, and more preferably 20 to 100%. If the shrinkage is too low, to use for shrink wrap and shrink wrap packaging,
This is because it tends to be insufficient. In general, the shrinkage rate of the polylactic acid-based shrinkable sheet is about 10% in shrink wrapping and shrink wrapping, and the shrinkage rate of 30% or more in the case of labels such as PET bottles. Good.

In order to make the contraction rate 30% or more, ΔHm−ΔHc should be set to 5-20 J, which is smaller than the above range.
/ G is preferred. By doing this,
This is because the degree of shrinkage of the polylactic acid-based shrinkable sheet can be further increased.

The polylactic acid-based shrinkable sheet obtained according to the present invention can be used as a packaging material or a shrinkable label material. Containers, foods such as fresh foods, and the like are used as objects to be packaged using the packaging material and the shrinkable label material. Examples of the container include a container having a high hardness such as a glass bottle, a glass container, and a hard plastic container, and a container formed of paper, a plastic having a low hardness such as polystyrene, polyethylene, and polyethylene terephthalate. These containers are used for any purpose such as food, beverage, and medicine.

The object to be packaged is shrink-wrapped or shrink-wrapped by the above-mentioned packaging material. At this time, since the polylactic acid-based shrinkable sheet has a sufficient shrinkage ratio and no thickness unevenness at the time of stretching, the shrink-wrapping finish is good when shrink-wrapped and the appearance is good in the packaged state. Furthermore, even if a heat treatment is performed after packaging, the packaging materials do not fuse with each other, so that handling becomes easy. In addition, since the above-mentioned polylactic acid-based shrinkable sheet material has good printing performance and can be printed neatly, when used as a shrinkable label material, first, after printing on the above-mentioned polylactic acid-based shrinkable sheet material, it is coated. By shrinking and adhering to the packaging material, it can be effectively used as a label.

[0038]

The present invention is not limited by the following examples. Table 1 and Table 2
In the above, "L / D ratio" indicates the composition ratio of L-lactic acid and D-lactic acid constituting the polylactic acid-based polymer. Also, "Mw"
Represents the weight average molecular weight of the polylactic acid-based polymer. Also,
The measurements and evaluations shown in the examples were performed under the following conditions.

(1) Measurement of heat of crystal fusion (ΔHm) Measurement was made using a polylactic acid-based polymer itself having a predetermined L / D ratio, which is a component of a biodegradable polymer forming a sheet.

First, from the melting point of the polylactic acid-based polymer, 3
The polylactic acid-based polymer was heat-treated at a temperature lower by 0 ° C. for 2 hours to crystallize the polylactic acid-based polymer. Then, using DSC-7 manufactured by Perkin-Elmer, 10 mg of the above crystallized polylactic acid-based polymer was subjected to JIS-K7
Based on 122, ΔHm was determined from the area of the endothermic peak when the temperature was increased at a rate of 10 ° C./min.

(2) Measurement of heat of crystallization (ΔHc) A 10 mg sheet sample was heated at a rate of 10 ° C./min based on JIS-K7122 using DSC-7 manufactured by PerkinElmer. ΔHc was determined from the area of the exothermic peak.

(3) Heat Shrinkage Rate The test direction of the sample of the sheet was measured in the longitudinal direction (hereinafter, referred to as the longitudinal direction).
Abbreviated as "MD". ) Was cut out into 140 mm × 10 mm, a rating line between 100 mm was put in the MD, immersed in a hot water bath at 80 ° C. for 10 seconds, the dimension between the rating lines was measured, and the heat shrinkage was calculated according to the following equation.

Heat shrinkage (%) = ｛(dimension before shrinkage) −
(Dimension after shrinkage) / (dimension before shrinkage) x 100 In Tables 1 and 2, TD indicates the width direction of the sample.

(4) Fusing test The sheet material was cut into a size of 60 mm in length and 30 mm in width and overlapped, and a pressure of 1.5 kgf / kg was applied by a heat sealing machine.
The state of fusion of the film when heated at 80 ° C. for 10 seconds in cm ² was examined. In addition, when easily peeled off by hand, ○, when it is slightly fused, △, and when it is hard to be peeled off, ×
Displayed with.

(5) Measurement of Tg Using Perkin-Elmer DSC-7, a 10 mg sheet sample was glass transition from a thermogram when the temperature was raised at a rate of 10 ° C./min based on JIS-K7122. A point (Tg) was determined.

(6) Comprehensive Evaluation The obtained polylactic acid-based shrinkable sheet was comprehensively evaluated from various physical properties and a fusion test. The symbols in Tables 1 and 2 mean the following. ◎: Good performance as a whole ○: Somewhat good performance as a whole ×: Not good performance as a whole

Example 1 L-lactic acid: D-lactic acid = 90:
A polylactic acid-based polymer having a structural unit of 10 and a weight average molecular weight of 180,000 is extruded from a T-die at 210 ° C. by a 30 mmφ uniaxial extruder, quenched by a castin gluer, and unstretched sheet having a thickness of 220 μm I got The obtained unstretched sheet was stretched 4.4 times in the width direction at 77 ° C. to obtain a polylactic acid-based shrinkable sheet. The ΔHm, ΔHc and heat shrinkage of the obtained polylactic acid-based shrinkable sheet were measured, and a fusion test was performed. Table 1 shows the results.

(Examples 2 to 5, Comparative Examples 1 to 4) Except that a polylactic acid-based polymer having a constitutional unit having the ratio of L-lactic acid to D-lactic acid shown in Table 1 or Table 2 was used. In the same manner as in Example 1, a polylactic acid-based shrink film was obtained. The ΔHm, ΔHc and heat shrinkage of the obtained polylactic acid-based shrinkable sheet were measured, and a fusion test was performed. The results are shown in Table 1 or Table 2.
Shown in

Example 6 L-lactic acid: D-lactic acid = 90:
100 parts by weight of a polylactic acid-based polymer having a structural unit of 10 and a weight-average molecular weight of 180,000, as a biodegradable aliphatic polyester, Bionole # 3 manufactured by Showa Polymer Co., Ltd.
003 (trade name) (Tg = −45 ° C.) 25 parts by weight, and the mixture is mixed with a 30 mmφ single-screw extruder.
The sheet was extruded from a T-die at 200 ° C. and quenched by a castin gluer to obtain an unstretched sheet having a thickness of 220 μm.
The obtained unstretched sheet was stretched 4.4 times in the width direction at 77 ° C. to obtain a polylactic acid-based shrink film. The ΔHm, ΔHc and heat shrinkage of the obtained polylactic acid-based shrinkable sheet were measured, and a fusion test was performed. Table 1 shows the results.

[0050]

[Table 1]

[0051]

[Table 2]

[0052]

According to the present invention, a biodegradable polylactic acid-based shrinkable sheet having a sufficient shrinkage can be provided.

When used for labels such as bottles for beverages, it is possible to provide a biodegradable polylactic acid-based shrinkable sheet which does not fuse with each other during heat sterilization.

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Claims (7)

[Claims] 1. A sheet formed from a biodegradable polymer containing a polylactic acid-based polymer as a main component, wherein the polylactic acid-based polymer has a heat of crystal fusion (ΔHm) of 5 to 45 J /.
g, and when the sheet is heated, the heat of crystallization (ΔHc) generated by crystallization of the polylactic acid-based polymer which is a constituent component of the biodegradable polymer forming the sheet.
And ΔHm, that is, ΔHm−ΔHc is 5 to 5.
A polylactic acid-based shrinkable sheet having a weight of 32 J / g. 2. The polylactic acid-based shrinkable sheet according to claim 1, wherein ΔHm is 20 to 40 J / g. 3. The polylactic acid-based shrinkable sheet according to claim 1, wherein ΔHm−ΔHc is 10 to 30 J / g. 4. The composition ratio of L-lactic acid to D-lactic acid, which is a component of the polylactic acid-based polymer, is 98: 2 to 94: 6 or 6:94 to 2:98. Claim 1
4. The polylactic acid-based shrinkable sheet according to any one of items 1 to 3. 5. A shrinkage rate at 80 ° C. for 10 seconds of 10
% Or more, the polylactic acid-based shrinkable sheet according to any one of claims 1 to 4. 6. A packaging material using the polylactic acid-based shrinkable film according to any one of claims 1 to 5. 7. A shrinkable label material comprising the polylactic acid-based shrinkable film according to any one of claims 1 to 5.